Acinetobacter baumannii-calcoaceticus complex and other members of this species frequently colonize the human skin without harm. However, injuries to the skin from scrapes, wounds or surgery, can result in Acinetobacter infection of the wound, blood, soft tissues, and central nervous system. Given that >80% of Acinetobacter sp. are also multiply drug resistant (MDR) (at least three classes of antibiotics), these infections may result in adverse clinical outcomes, including high rates of morbidity and mortality, prolonged hospital stay, and substantial health care expenses. Military personnel and athletes have an increased the risk of injuries (from skin abrasions to severe wounds) that would be susceptible to infection by Acinetobacter spp., thus methods to remove them quickly and effectively would reduce or eliminate downstream complications. Outbreaks caused by MDR Acinetobacter have been reported in hospitals all over the world; more recently, they have become a serious problem in military medical facilities. Because of its MDR, Acinetobacter infections are difficult to treat so infections by these organisms usually result in a poor outcome. Thus, new and better ways of controlling this pathogen are needed.
Acinetobacter baumannii strains resistant to all known antibiotics have now been reported. Acting in synergy with this emerging resistance profile is the uncanny ability of A. baumannii to survive for prolonged periods throughout a hospital environment, thus potentiating its ability for nosocomial spread. The organism commonly targets hospitalized subjects, who are critically ill with breaches in skin integrity and airway protection. As such, hospital-acquired pneumonia is still the most common infection caused by A. baumannii. However, recently, infections involving the central nervous system, skin and soft tissue, and bone have emerged as highly problematic for certain institutions. Because of this resistance problem, new methods to control these pathogens must be developed.
Antimicrobial agents known as bacteriophage-encoded lysins have been identified. Bacteriophages are viruses that infect bacterial and it is estimated that there are 106 distinct bacteriophage species. Bacteriophage lysins are generally genus- or species-specific, i.e., a Staphylococcus aureus phage lysin may have activity only against Staphylococcus aureus providing a targeted therapeutic approach. In some cases, lysins may have activity against several genera or species.
Bacteriophage infect their host bacteria to produce more virus particles. At the end of the reproductive cycle they are faced with a problem, how to release the progeny phage trapped within the bacterium. They solve this problem by producing an enzyme called “lysin” that degrades the cell wall of the infected bacteria to release the progeny phage. The lytic system consists of a holin and at least one peptidoglycan hydrolase, or lysin, capable of degrading the bacterial cell wall. Typically, the holin is expressed in the late stages of phage infection forming a pore in the cell membrane, allowing the lysin(s) to gain access to the cell wall peptidoglycan resulting in release of progeny phage. Significantly, exogenously added lysin, in the absence of a holin, can lyse the cell wall of healthy, uninfected cells, producing a phenomenon known as “lysis from without”.